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🌲 How does a tree move water to its top leaves?

Leaf evaporation tensions a continuous water column in xylem — ascent without a trunk heart.

lessons

~10 min

to learn

🔬 Science

subject

Adults

level

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What you’ll learn

The continuous water columnExplain cohesion-tension: continuous water in xylem pulled by leaf evaporation.Trees lack a trunk heart. Hydrogen-bonded water in xylem is tensioned when leaves lose vapor, lifting soil water to the canopy.
Leaves open the valveLink stomata, root intake, and weather to the hydraulic bill of photosynthesis.Stomata admit CO₂ and lose water. Roots supply the column; dry windy air raises demand until pores partially close.
When the rope snapsName cavitation risk, height limits, and the xylem/phloem distinction.Embolisms break flow under extreme tension. Height is hydraulically constrained. Sugars ride phloem, not the same tensioned rope.

Questions this course answers

What mainly pulls water to the top leaves of a tall tree?

Transpiration from leaves tensions a continuous water column held by cohesion (and adhesion to xylem walls); there is no trunk heart driving tall ascent.

Order the simplified path of water through a transpiring tree

Uptake, conduit transport, evaporative loss, and continued pull form a loop linking soil to air.

Match each term to its role

Xylem handles ascent of water; stomata set evaporative demand; cavitation disables conduits; phloem is a separate sugar highway.

Grounded in trusted sources

Tyree & Zimmermann, Xylem Structure and the Ascent of Sap (cohesion-tension framework)
Taiz et al., Plant Physiology and Development — water relations and xylem chapters
USDA Forest Service / university extension summaries of transpiration and drought cavitation
Nobel, Physicochemical and Environmental Plant Physiology — water potential basics

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